The present invention relates in general to cell preservation techniques and, in particular to a new and useful process and apparatus which utilizes dialysis processing to preserve living cells and cell components, particularly red blood cells.
Red blood cells, which have been frozen in the presence of glycerol, can be stored for years at -80.degree. C. with excellent post-thaw recovery and in vivo survival.
Today, three approaches to red cell freezing and deglycerolization are in clinical use: the agglomeration method, the low glycerol method and the high glycerol procedure as modified and adopted by the American Red Cross. Estimates of the extent to which these three procedures are used in North America, based on sales of glycerol solutions during 1976 by U.S. manufacturers, total 25,000 units processed by agglomeration, 30,000 by the low glycerol method and 165,000 by the high glycerol procedure. All procedures yield a product of essentially equivalent quality. Differences in the rate of use to some extent reflect differences in processing costs as well as the very large impact of the Red Cross Blood Program which processes an estimated 50% of all units frozen in North America.
Of all the users for frozen red blood cells, probably the most important and far reaching is their use for inventory control. First, in regional blood centers, cells collected during peak collection times of the year could be maintained in storage for use in times of deficit. Second, small isolated hospitals, because of irregular needs, now must either tolerate an excessive rate of outdating or engage in an extensive exchange program with a distant regional center. Frozen red cells would be a solution for both of these inventory control problems but only provided that the glycerolization procedure was rapid, simple and economical.
Some of the problems surrounding the removal of glycerol from the high glycerol preparations have been overcome through the use of cell washing devices. One of these, developed by the Haemonetics Company (Braintree, MA) and based on the Cohn Fractionator, performs a continuous flow wash in a disposable bowl. The other apparatus developed by the IBM Corporation, conducts an automated batch wash in a disposable bag. Although effective, these devices add considerable cost to the use of frozen cells.
At the present time, the capital equipment ranges from over $5,000 to over $17,000 with the disposable plastic components ranging from about $8.00 to over $20.00. The washing protocols require a minimum of 30 minutes per unit and these devices will wash only a single unit at a time. The time required for processing of frozen red blood cells using current methods is an effective obstacle to the use of frozen red cells for emergency applications under most circumstances. On the other hand, when frozen cells are routinely deglycerolized on a large scale within a hospital, the diversion of deglycerolized cells for emergency use appears to be entirely feasible, and at least two large general hospitals have reported outdating rates of 5% and 1% or less. See Meryman, H. T., Am. Journal of Med. Tech. 41:265-282, 1975 and Huggins, C. E., In: Red Cell Freezing, AABB Workshop, PP. 31-53, 1973.
The 24 hour outdating period constitutes one of the major problems with frozen red cells today. This is particularly true when cells are deglycerolized at a blood center and delivered to a hospital at some distance. A unit of cells specifically directed to a particular patient, and then not used, frequently cannot be crossmatched for some other recipient within the 24 hour limit. The 24 hour outdating is imposed because of the hazard of bacterial contamination during processing.
Processing of multiple units imposes a special hardship where more than one unit has been deglycerolized in the Haemonetics disposable bowl. Blood centers preparing frozen red cells under Federal license are required to use a variety of safeguards to assure that all units washed through the same bowl are delivered to a single recipient. Changes in the design of the Haemonetics apparatus could obviate the need to prepare multiple units with the same bowl. Acceptable economics, however, and more rapid and simultaneous deglycerolization are a necessary goal of blood banking.
Cost continues to be the predominant disadvantage of frozen red cells, although one large general hospital reports that, since converting almost entirely to frozen or washed red cells, the cost per thousand units of matched, frozen cells is only 44% more than matched whole blood. At the present time, disposable supplies for glycerolization and deglycerolization total at least $35.00 per unit. The present scale of red cell freezing is already sufficient to obtain cost reductions from volume production and it seems unlikely that substantial further reductions in the costs of disposables can be anticipated.
Another problem which adds to the cost of frozen red blood cells (RBC) is the rate of hemolysis that is the destruction of RBC's due to rupturing of the cell membranes. Hemolysis during deglycerolization accounts for up to 12% loss of the red blood cells. The various sterile solutions used in RBC washing lowers the osmolality too fast for the cells to accommodate and the cells rupture. These losses are also obviously a major cost factor.
All methods of long term storage of glycerolized red blood cells require freezing between -10.degree. C. and -80.degree. C. There is a significant problem associated with maintenance of such low temperatures in special freezers. Should a power failure occur, in order to preserve the stored blood, emergency power units are required. If the freezer fails, substantial loss of stored blood may occur.